This invention relates to the polymerization of olefins, and more particularly, to improved, highly active catalysts and catalyst components therefor.
It is well known to polymerize olefins using catalysts generally comprising an organometallic activator and a supported, transition metal-containing component; and such catalysts often exhibit highly desirable performance in the polymerization of olefins in that the same are sufficiently active that commercially useful products can be obtained without the need for separation of catalyst residues from the polymeric product. Typically, the supported component of such catalysts is prepared by reaction of a liquid, transition metal-containing component with a solid support material, such as a metal oxide or salt, to form a solid catalyst component which is activated with an organometallic activator such as an aluminum alkyl or alkylaluminum halide. For example, U.S. Pat. No. 3,644,318 (Diedrich et al.) discloses highly active catalysts comprising an organoaluminum activator and a supported component prepared by reaction of solid magnesium alcoholate with liquid, halogen-containing compounds of titanium (IV), optionally followed by reaction of the result with an organoaluminum component. U.S. Pat. No. 3,901,863 (Berger et al.) discloses highly active catalysts wherein the supported component is prepared by reaction of liquid, oxygenated organic transition metal-containing component, such as a tetraalkyl titanate, with a solid, oxygenated organic divalent metal compound and alkylaluminum halide.
While such catalysts often exhibit desirably high activities, polymerization performance typically is not satisfactory in all respects because numerous polymer properties are affected by the choice of catalysts. For example, polyolefin processability can vary substantially depending upon polymer molecular weight and molecular weight distribution, both of which are influenced by the choice of catalyst. Polymer particle size and bulk density also vary depending upon the choice of catalyst. In terms of process efficiency, highly active catalysts such as those described hereinabove give important advantages in terms of eliminating the need for removal of catalyst residues; however, process efficiency can suffer in other respects. For example, preparation of the above described supported catalyst components is disadvantageous because both solid and liquid phases are present during preparation. In order to ensure adequate reaction between the solid and liquid reactants it often is necessary to employ a substantial excess of the liquid reactant as well as vigorous agitation and/or high temperatures in preparation.
Efforts to avoid the above-described difficulties while maintaining desirable polymerization performance in other respects have met with varying degrees of success. U.S. Pat. No. 3,989,881 (Yamaguchi et al.) discloses supported catalyst components of the formula EQU [Mg.sub.n M.sub.1-n ]X.sub.m .multidot.xY
wherein M is titanium or vanadium, X is halogen, Y is ether, 0.01.ltoreq.n.ltoreq.0.99, 2&lt;m&lt;4 and 1&lt;x&lt;3, which are prepared by reaction of (1) an ether solution of a titanium or vanadium halide-ether complex with (2) an ether solution of a magnesium halide-ether complex. The disclosed supported catalyst components can be combined with organoaluminum component to form a catalyst having sufficiently high activity that elimination of catalyst residues is unnecessary; however, polyolefin molecular weight distributions are narrow according to the patentee and, although the disclosed preparative method avoids problems associated with contacting solid and liquid phases, the preparation is disadvantageous in that extra steps are required for preparation of the titanium or vanadium halide- and magnesium halide-ether complexes. Further, preparation of such catalyst components is costly due to the use of electron donors as solvents.
U.S. Pat. No. 4,124,532 (Giannini et al.) discloses supported catalyst components of the formula EQU M.sub.m M'X.sub.2m Y.nE
wherein M is magnesium, manganese and/or calcium, m ranges from 0.5 to 2, M' is titanium, vanadium and/or zirconium, X is chlorine, bromine or iodine, Y is halogen, oxygen or specified oxygen-, nitrogen- or sulfur-containing organic groups, n ranges from 0.5 m to 20 m and E is a selected electron donor. Such catalyst components are prepared by mixing electron donor solutions of MX.sub.2 and M'Y to form a liquid reaction product followed by evaporation of the electron donor solvent to recover a solid catalyst component. Similar to the supported catalyst components of Yamaguchi et al., those of Giannini et al. offer advantages in terms of avoiding a two phase preparation system; however, the use of electron donor as a solvent and the fact that an evaporation step is necessary to recover a solid reaction product from the electron donor solvent add cost to the preparation of the supported components. Further, olefin polymerization activity of catalysts containing the disclosed supported components and an organoaluminum component is relatively low as shown in the patentee's examples.
Other proposals which may be of interest with respect to the present invention include those directed to preparation of supported catalyst components by reaction of transition metal-containing components with support materials prepared by contacting various divalent metal compounds with electron donors to modify various catalyst properties. For example, U.S. Pat. No. 3,642,746 (Kashiwa et al.) discloses supported components prepared by contacting a transition metal-containing component with a solid support material prepared by contacting divalent metal halide with electron donor. According to the patentee, contacting of the metal halide with electron donor results in improved activity in polymerization of olefins. U.S. Pat. No. 3,647,772 (Kashiwa) discloses similar supported catalyst components except that the support material is a solid obtained by contacting magnesium carbonate with electron donor. U.S. Pat. No. 3,694,421 (Vetter) discloses supported catalyst components of improved polymerization activity prepared by reaction of a halogen containing titanium (IV) compound with the solid reaction product of a hydroxyl group-containing mangesium compound, e.g., Mg hydroxide, hydroxychloride, or carboxylate, with an aldehyde. U.S. Pat. No. 4,115,319 (Scata et al.) discloses stereospecific supported catalyst components prepared by reaction of titanium tetrachloride with a solid support material obtained by reaction of a halogenating agent with a magnesium compound such as an alcoholate, carboxylate, a Grignard compound or a dihydrocarbylmagnesium compound, and treatment with electron donor.
Despite the foregoing proposals, there remains a need for improved, highly active olefin polymerization catalysts having a desirable balance of properties and offering flexibility from a preparative standpoint. It is an object of this invention to provide an improved supported catalyst component for olefin polymerization and catalyst based thereon. A further object of this invention is to provide olefin polymerization catalysts which exhibit sufficiently high activites that commercially useful polymeric products can be obtained without removal of catalyst residues therefrom. A further object of the invention is to provide olefin polymerization catalysts which are sensitive to hydrogen such that a single catalyst can be used to prepare a wide variety of product grades. A further object of the invention is to provide a support catalyst component which offers advantages in terms of preparative flexibility in that either a solid-liquid or liquid-liquid preparative system can be utilized.
We have found that the objects of this invention can be attained through the use of support materials prepared by reaction of components comprising at least one magnesium alcoholate and at least one halocarboxylic acid in preparation of supported, olefin polymerization catalyst components. Advantageously, such support materials can be obtained in either hydrocarbon-soluble or -insoluble form such that on combination with a liquid transition metal-containing component, either a solid-liquid or liquid-liquid preparative system is attained without the need for expensive solvents. Further, in the liquid-liquid system, the reaction product of the support material and transition metal component often is a solid which precipitates readily from the reaction mixture such that expensive recovery operations are not required. Catalysts comprising (1) the solid reaction product of components comprising the above-described support material and Group IVB and VB metal-containing component and (2) organometallic promoter exhibit sufficiently high olefin polymerization activities that removal of catalyst residues from the polymeric products is unnecessary. Further, the invented catalysts are sensitive to hydrogen so that controllable variations in polymer molecular weights, and accordingly polymer melt flow rates, are easily attained. In addition, polyolefins prepared using such catalysts exhibit molecular weight distributions well suited for molding applications.